1. Technical Field
The present invention relates to a multilayer circuit board and, more particularly, to a multilayer circuit board in which a signal wiring, a ground wiring, and a power supply wiring are provided at a high density.
2. Related Art
In recent years, with increasing the operating speed of electronic devices, high-frequency use highly-integrated semiconductor elements (hereunder sometimes referred to simply as high-frequency elements), whose operating frequency exceeds 4 GHz, have appeared. Thus, wiring-boards, on which high-frequency elements are mounted, have been required to be less mixed with noises and to excel in high-frequency characteristics. On the other hand, there have been strong demands for miniaturization of electronic devices, on which high-frequency elements are mounted. Accordingly, the wiring board, on which a high-frequency element is mounted, needs to increase the density of wirings provided therein and to reduce the size thereof.
Generally, a wiring board, on which a high-frequency use semiconductor element is mounted, has a multilayer structure. In each of wiring-layers of the multilayer structure, signal wirings, ground wirings, and power supply wirings are formed. (Hereinafter, wiring boards each having a multilayer structure will be referred to as multilayer wiring boards). Electrical inter layer connection is performed using via holes.
To downsize (or reduce the plane area of) a multilayer wiring board of such a configuration, it is necessary to achieve a high density of wirings by making signal wirings, ground wirings, power supply wirings close to one another so as to provide a narrow pitch of the wirings. Additionally, in the case of the multilayer wiring board, on which a high-frequency device is mounted, a high-frequency signal is supplied to the signal wiring. Accordingly, to enhance transmission efficiency, it is necessary to perform matching of the characteristic impedance of the signal wirings by configuring the multilayer wiring board to have, for example, a microstrip line structure or a coplanar structure (see, for instance, Patent Documents 1 and 2).
FIGS. 8A to 10C illustrate an example of such a kind of a related multilayer wiring board. FIGS. 8A, 8B, 9A and 9B illustrate a multilayer wiring board 100A which is a first example of the related multilayer wiring board. FIG. 8A enlargedly illustrates the vicinity of a position, at which a semiconductor chip 101 is mounted, of the multilayer wiring board 100A. FIG. 8B illustrates a cross-section taken along line B1-B1 shown in FIG. 8A (i.e., a cross-section in which the semiconductor chip 101 is mounted).
As illustrated in FIGS. 8A and 8B, the first related multilayer wiring board 100A is configured so that the semiconductor chip 101 is mounted thereon by flip-chip-bonding. Therefore, a signal electrode 115, a power supply electrode 116, and a ground electrode 117, to which bumps 102 provided on the semiconductor chip 101 are connected, are formed on the top surface of the multilayer wiring board 100A. A signal wiring 125 is connected to a signal electrode 115. A power supply wiring 126 is connected to a power supply electrode 116. A ground wiring 127 is connected to a ground electrode 117 (i.e., the power supply wiring 126 and the ground wiring 127 are not shown in FIGS. 8A and 8B).
The multilayer wiring board 100A has a multilayer structure shown in FIGS. 9A and 9B. More specifically, as illustrated in FIG. 9B, the multilayer wiring board 100A has a four-wiring-layer structure including, in order from a top-most layer, the following arranged layers, a first wiring layer 112A, a first insulating layer 111A, a second wiring layer 112B, a second insulating layer 111B, a third wiring layer 112C, a third insulating layer 111C, and a fourth wiring layer 112D.
FIG. 9A illustrates the first wiring layer 112A formed on the first insulating layer 111A. The first wiring layer 112A is configured so that the signal electrode 115, the power supply electrode 116, the ground electrode 117, the signal wiring 125 electrically connected to the signal electrode 115, and the ground wiring 127 electrically connected to the ground electrode 117 are pattern-formed.
FIGS. 10A to 10C illustrate a second related multilayer wiring board 100B. The multilayer wiring board 100B has a three-wiring-layer structure. More specifically, as cross-sectionally illustrated in FIG. 10C, the multilayer wiring board 100B has, in order from a top-most layer, the following arranged layers, that is, a first wiring layer 112A, a first insulating layer 111A, a second wiring layer 112B, a second insulating layer 111B, and a third wiring layer 112C.
FIG. 10A illustrates the first wiring layer 112A. As illustrated in FIG. 10A, the first wiring layer 112A is configured to form a signal wiring 125 between paired ground wirings 127. Thus, the first wiring layer 112A has a coplanar structure.
FIG. 10B illustrates a second wiring layer 112B. As illustrated in FIG. 10B, the second wiring layer 112B has a structure in which a signal wiring 125, a power supply wiring 126, and a ground wiring 127 are mixed.
Thus, a wiring density can be increased by multilayerization of circuit boards to thereby obtain the multilayer wiring boards 100A and 100B. Also, as illustrated in FIG. 9B, between the first wiring layer 112A and the second wiring layer 112B, the signal wiring 125 and the ground wirings 127 of the multilayer wiring board 100A constitute a microstrip line structure. As illustrated in FIG. 10C, between the second wring layer 112B and the third wiring layer 112C, the signal wiring 125 is provided among the ground wiring 127 and the power supply wiring 126. Thus, the multilayer wiring board 100B has a strip line structure. Accordingly, even in the related multilayer wiring boards 100A and 100B, impedance matching is appropriately performed. Consequently, electrical characteristics can be improved.
[Patent Document 1] JP-A-2002-093940
[Patent Document 2] JP-A-2004-140295